Disseminated infection due to organisms of the Mycobacterium avium complex (MAC) has been found in as many as 50% of patients with late stage AIDS in the United States and is associated with disabling systemic symptoms and shortened survival. As patients with AIDS survive longer, MAC epidemiology of disseminated MAC is not well-understood. MAC is present in the environment, especially in natural water sources and hospital water supplies, but risk factors for acquisition have not been studied. Little is known about its prevalence in AIDS outside the United States, though it is to be less common in European countries where BCG is administered, and in African countries where tuberculosis is prevalent. However, sensitive diagnostic methods (i.e. lysis-centrifugation blood cultures) have not been applied to detect disseminated mycobacterial infections (including MAC and BCG) among AIDS patients in all of these areas. The aims of the present study are (i) to determine the prevalence of disseminated MAC among AIDS patients at 5 geographic sites (Kenya, Zaire, Finland, Boston, New Hampshire), (ii) to identify risk factors for the development of disseminated MAC, (iii) to identify the specific environmental source of disseminated MAC and (iv) to determine the prevalence of disseminated BCG infection in AIDS. Four studies will be conducted at each of the 5 sites: 1.Environmental samples will be cultured for MAC. 2.Normal adult subjects will be skin tested with M. avium and M. tuberculosis antigens to determine population exposure rates at each organism. 3.Patients with late stage HIV infection will have lysis-centrifugation blood cultures performed for mycobacteria (MAC and BCG) and will be interviewed for exposure histories. Patients with positive blood cultures for MAC will be matched with negative blood cultures for MAC in a case control study of risk factors. The prevalence of disseminated BCG infection will also be determined (in Kenya, Zaire and Finland). 4.A molecular epidemiologic analysis of all human and environmental MAC isolates will be performed using phenotypic markers, plasmid profiles, and chromosomal DNA restriction polymorphisms.